Microwave antenna and mounting and stabilizing means therefor



Feb. 12, 1952 c. L. NORDEN 2,585,579

MICROWAVE ANTENNA AND MOUNTING AND STABILI ZING MEANS THEREFOR Original Filed Sept. 25, 1945 4 Sheets-Sheet l INVENTOR. CARL L, A/oeas/v Feb. 12, 1952 c, NQRDEN 2,585,579

MICROWAVE ANTENNA AND MOUNTING AND STABILIZING MEANS THEREFOR Original Filed Sept. 25, 1945 4 Sheets-Sheet 2 IN VEN TOR. CW4 A. A/oeas/v HTT PA/EY Feb. 12, 1952 c. 1.. NORDEN MICROWAVE ANTENNA AND MOUNTING AND STABILIZING MEANS THEREFOR Original Filed Sept. 25, 1945 4 Sheets-Sheet 3 INVENTOR. L A/o/aafn/ arrow/5y Feb. 12, 1952 C. L. NORDEN MICROWAVE ANTENNA AND MOUNTING AND STABILIZING MEANS THEREFOR Original Filed Sept. 25, 1945 4 Sheets-Sheet 4 Patented Feb. 12, 1952 UNITED STATES vPATENT OFFICE MICROWAVE ANTENNA MOUNTING AND STABILIZING S THEREFOR Carl L. Norden, New York, N. Y., assignor to The N orden Laboratories Corporation, White Plains, N. Y., a corporation of Connecticut 13 Claims.

My invention relates to a microwave antenna and mounting and stabilizing means therefor.

This application is a division of my copending application Serial No. 618,448 filed September 25, 1945, for Stabilization of Directional Devices, now Patent No. 2,499,228.

In the use of microwaves, such as in radar in aircraft in connection with navigation, bombing, and the like, it becomes necessary to control and stabilize the antenna in three axes. these axes is the azimuth axis, that is the axis around which the airplane yaws. The second is the cross-level axis which is the axis along the line of the microwave beam corresponding to what would be the line of sight if the device were an optical instrument. The third axis about which stabilization must take place is the level axis which is one perpendicular to the cross-level axis and extending in a horizontal direction. The cross-level axis is one around which roll along the line of sight takes place and the level axis is one about which pitch along the line of sight takes place. It is desirable too to produce a conical scanning of the radar beam and this requires that the antenna reflector be rotated with respect to the microwave feed horn.

One object of my invention is to provide a microwave antenna, a mounting therefor, and means for stabilizing the antenna about three axes disposed at right angles to each other.

Another object of my invention is to provide a stabilized microwave antenna in which conical scanning of a radar beam may be achieved while avoidin objectionable vibrations.

Another object of my invention is to provide a stabilized microwave antenna provided with conical scanning means for the radar beam which reduces gyroscopic forces to a minimum.

Another object of my invention is to provide a microwave antenna, a mounting therefor and stabilization and control means.

' Other and further objects of my invention will appear from the following description.

In the accompanying drawings which form part of the instant specification, and which are to be read in conjunction therewith:

Figure 1 is a perspective view of a stabilization and control apparatus of a radar antenna of the horn and reflector type, showing one embodiment of my invention.

Figure 2 is a view similar to Figure 1 with parts broken away to show details of construction.

Figure 3 is a detail view of the antenna horn and the mounting frame for the reflector drawn in the same orientation as shown in Figure 1 but The first of its construction.

Figure 4 is a side elevation of the parts shown in Figure 3 with the antenna in position.

Figure 5 is a rear elevation of the assembly shown in Figure 4.

Figure 6 is a schematic view showing the circuits used in controlling the apparatus of Figure 1.

Referring now to Figure l, the vertical axis around which control in azimuth is achieved is indicated by the arrow Z. The cross-level axis along the radar beam is indicated by the arrow X. The level axis at right angles to the crosslevel axis is indicated by the arrow Y. The antenna comprises a feed horn l0 rigidly attached to a frame 22 as can readily be seen by reference to Figures 1 and 3. The frame 12 is provided with lugs is, shown in Figures 3, 4 and 5. The lugs M are provided with openings Iii so that the frame i2 may be mounted for pivotal movement around the level or Y axis. The antenna reflector I8 is carried by the frame l2 through a plurality of cranks 20, 22, and 24, and their associated crank pins 26, 28, and 30, so that the antenna may be given a rotary motion providing the desired conical scanning of the radar beam, as will be described more fully hereinafter. An H-Irame 32 carries the axis around which the frame I2 is pivoted. The frame 32 is mounted about an axle 34 so that the frame may pivot about the cross-level or X axis. The axle 34 is carried by a block 36 which is in turn supported by a post 38 which is rotatably mounted about the azimuth axis or Z axis. The movement of the antenna assembly about the level axis Y and the movement of the H-frame 32 about the crosslevel axis X are controlled by a vertical gyroscope unit, indicated generally by the reference numeral 40, carried in a housing 42 secured to the H-irame 32. The control isimplemented by servomotors controlled by the gyroscope. The rotation of the post 38 about the azimuth axis Z is controlled by an azimuth gyroscope unit, indicated generally by the reference numeral 44, positioned in a housing 46 which is carried by the main frame structure 48, which also supports the servomotor controlled by the azimuth gyroscope and the associated means for controlling the direction of the antenna in azimuth. The entire assembly may be mounted in an aircraft in any convenient position through means of the main frame 48.

The azimuth gyroscope may be of any suitable type and is well known to the art. It is adapted to stabilize a part such as gear 50 in azimuth. The gear 50 may be disconnected, if desired, by means of a clutch knob 52 through which the gear 50 is normally clutched to the part stabilized in azimuth by the gyroscope. The gear 50 meshes with an idle gear 54 which meshes with a gear 56 which is rotatably carried by the post 38. The gear 56 meshes with a gear 58 which is fixed to a shaft 60 which controls a servomotor 82 secured to a bracket 84 which is secured to the post 38. The post 38 is rotatably mounted in housing 83 carried by the main frame 48. Accordingly, rotation of the servomotor 62 will rotate the bracket 64 and the post 38 and the associated structure supported thereby around the azimuth axis Z. It will be observed further that this rotation is controlled by the azimuth gyroscope. In other words, if the servomotor 62 is stationary the post 38 will remain fixed in azimuth with relation to gear 50.

There are three potentiometers associated with the azimuth gearing. A turn follow-up potentiometer I58 is geared to the output of the servomotor 62 as can readily be seen by reference to Figure 2. This potentiometer will register angular movement of the post 38 around the Z axis with relation to the azimuth gyroscope. A drift angle potentiometer I2 is carried within the housing l which is mounted on the frame 48. This potentiometer is adapted to control crosstrail. The potentiometer shaft 14 is driven by gear I6 which is in mesh with gear sector 18 which is formed integrally with bracket 64, so that it moves with the bracket and hence with post 38. In this way the angle between shaft I4 and the potentiometer housing I0 will represent the drift angle, that is, the angle between the post 38 and the main frame 48. A third potentiometer 80 is carried by the main frame 48 and is driven from gear I6, and is so connected in the control circuit, as shown in Figure 6, as to register the differential angular movement of the post 38 with respect to the aircraft. By means of the circuit, shown in Figure 6, which will be described more fully hereinafter, the gearing and potentiometers are employed to control the antenna about the azimuth or Z axis and about the cross-level axis or X axis. If desired, refinements may be included, such as means for imparting a scanning movement about the azimuth axis to the antenna and the inclusion of follow-up motions therefor, which may be housed within the potentiometer housing I0. These refinements are not essential to the present invention and are accordingly not described.

Movement of the post 38 will rotate the entire axial system comprising the X axis and the Y axis about the Z axis. In other words, level and cross-level movements are referred to the line of the radar beam as distinguished from the direction of flight of the ircraft. Still referring to Figure 2, the post 38 terminates in a lower block 36 upon which the H-frame 32 is pivotally mounted by means of the shaft 34 as was pointed out hereinabove. The housing 40 for the vertical gyroscope unit is rigid with and forms part of the H-frame 32. A servomotor lodged within the housing 40 has an output gear 82 which meshes with the gear sector 84 which is formed integrally with the block 36 which in turn pivots about the axis shaft 34. Rotation of the gear 82 will rock the H-frame 32 about the crosslevel or X axis.

The gyroscope which is shown diagrammatically in Figure 2 comprises a ertical rotor 86 carried by an inner gimbal ring 88 which is in turn carried by an outer gimbal ring or Cardan 90. The Cardan is pivotally supported along a level axis by trunnions 82. The spin axis of the gyroscope is normally maintained in a vertical direction by an erecting bail 84. A potentiometer sector 96 is carried by the housing 40 and cooperates with a brush 98 carried by the erecting bail 94. The brush 08, therefore, is adapted to indicate motion of the H-frame 32 with respect to the gyroscope, that is, motion about the crosslevel or X axis, and thus permits the control thereof through the servomotor which drives gear 82, as described above.

Referring now to Figure 1, it will be seen that the angular position of the antenna assembly about the level or Y axis is controlled by a second servomotor (not shown) which is positioned within the lower part of housing 40. This servomotor is adapted to rotate a shaft I60 having a worm I02 meshing with a worm gear segment I04 formed as a lever pivoted about pivot pin I06. A link I08 is connected to an arm H0 secured to the frame I2 to rock the frame about the level or Y axis. The servomotor which operates worm I02 is controlled by the potentiometer brush H2, shown in Figure 2, which is carried by the Cardan and cooperates with the potentiometer sector H4 which is rotatably carried around one of the trunnions 92. The arm H6, the arm IE8, and the connecting link I20 insure that there is a fixed angular relationship between the position of the antenna assembly and the potentiometer sector H4.

It will be observed that the level, cross-level and azimuth axes do not intercept at a common point as is the case usually in gimbal Cardan suspensions, but that the intersection of the level and cross-level axes is spaced from the intersection of the cross-level and azimuth axes. This feature is of importance in view of the necessity of accommodating microwave guide joints, since microwave guides must be used in utilizing microwaves in radar. The microwave guide from the radar equipment (not shown and forming no part of this invention) leads to a stationary joint member I22 located above the post 38. A rotatable joint member I24 cooperates with the stationary joint member I22. A microwave guide I26, shown in Figure l, terminates in a microwave guide joint member I28, shown in Figure 2, which is stationary with respect to the block 36. The joint member I28 cooperates with a moveable joint member I30.

Angular wave guide bend section I32 leads the microwaves from the joint member I30 to the joint member I34 which is stationary with respect to the H-frame 32. The joint member I34 cooperates with joint member I36 to which the feed horn I0 communicates so that the feed horn is rotatable with the antenna unit and is supported by the member I38.

The three microwave guide joints comprising members I22 and I24, I20 and I30, and I34 and I30 are thus arranged upon the respective Z axis, X axis, and Y axis, and further are coincident therewith even though they are spaced from the intersections of pairs of axes. In this way I am enabled to make provision for the necessary mechanical movements.

While it is to be understood that the radar apparatus as such forms no part of the instant invention, it comprises suitable visual indicators, such as cathode ray oscilloscope screens or other suitable apparatus for indicating target coordinance or controlling antenna movements in accordance with such indications.

The antenna framestructure I2, shown in Figures 3, 4 and 5, comprises a triangular frame carrying rotatable cranks 20, 22, and 24. The antenna reflector I8 is carried by the crank pins 26, 28 and 30. One of the cranks 22 is driven by a motor 2|. Since each pair of cranks when connected to the antenna reflector constitutes a parallel motion device the reflector will be caused to execute a parallel crank movement. Since the crank pin 28 rotates, the antenna reflector will rotate as a whole moving in a small circle having a radius equal to the distance between the axis of rotation of the crank and the crank pin 28. This type of scanning movement is advantageous since it minimizes gyroscopic resistance of the reflector. The gyroscopic efiect due to reflector rotation may be considerable due not only to the mass of the reflector but due to the speed of scanning which may be, in the embodiment illustrated, in the vicinity of 2000 R. P. M. The gyroscopic effect due to the reflector rotation will tend to cause precession so that the resulting torque will place an additional load upon the azimuth gyroscope and other stabilizing and control members which would decrease the efliciency of the apparatus or require additional bulk by increased weight of the installation. Forexample, when the antenna is tilted downwardly about the Y axis, the gyroscopic effect will tend to make it precess about the Z axis thus generating a. torque which must be overcome by the azimuth gyroscope. The conical scanning arrangement I have shown reduces this undesirable effect to a minimum. I accomplish this by using a small crank radius positioned at a distance from the center of gyration of the reflector about the X axis, since gyroscopic resistance will vary in the proportion which the square of the crank radius bears to the square of the radius of gyration of the reflector about the X axis. The use of a large radius of gyration together with a small crank radius will give a small gyroscopic resistance.

To reduce the tendency to vibration, the antenna is dynamically counter-balanced by means of weights formed integrally with each of the cranks 20, 22, and 24, and by counter-balancing weights 20' and 24', as will readily be observed by reference to Figures 4 and 5. The weights and the proportions of the, weights are selected so that the forces on each of the crank shafts are balanced about the crank shaft axis and are also balanced longitudinally of the crank bearings. All bearing reactions are accordingly reduced to a minimum and the tendency to vibration due to rotation of the reflector upon the frame structure I2 is reduced to a minimum.

The apparatus shown in Figures 1 to 5, inclusive, may be utilized with any suitable control apparatus as, for example, one which is shown diagrammatically in Figure 6, to which reference is now made. The circuit diagram illustrates an A. C. follow-up circuit for the control of the antenna about the level or Y axis. The vertical gyroscope potentiometer sector H4 is connected across one-half of a split secondary winding I40 of a transformer indicated generally by the reference numeral I42, and a second potentiometer I44 having a brush I46 is connected across the other half of the same winding by means of conductors I41, I48, I49, and conductor I50.

The brushes II2 and.I46 of these two potentiometers are connected through equal resistors I52 and I54 to an input connection I56 of a phase sensitive amplifier indicated diagrammatically by the reference numeral I58. The other connection to the amplifier I58, that is, conductor I60, is connected to conductor I49 and thence to the center tap of the secondary transformer winding I40. The

output signal of the amplifier I58 is impressed by conductors I62 and I64 to a two-Way relay I66 through which the servomotor which drives the shaft I00 of Figure l and its worm I02 is controlled. When the brushes I46 and H2 are in corresponding position upon their resistor sectors I44 and H4, the voltages. impressed across resistors I52 and I54 will be equal and opposite thus giving a null input to the amplifier I58. In this condition the servomotor is stationary. If the brushes I46 and H2 are not in a position to produce equal and opposite signals across the resistors I52 and I54, the resultant voltage to the input of the amplifier I58 will be of a value corresponding to the unbalance of position between the brushes and will agree in phase with the brush which is farther from the center tapend of its potentiometer. The relay I66 will be operated in a direction agreeable to the signal created by the difference in position between the brushes H2 and I46, so as to cause the servomotor to rotate the antenna assembly about the level or Y axis and thus through arm IIB, link I20. and arm H6 and rebalance the potentiometer II4 with the potentiometer I44. The potentiometer I44 may be controlled in any convenient manner as, for example, by coupling it to a bomb sight computer part designed for rotating the telescope mirror or prism of an optical sight in elevation. In this manner it will be. readily apparent that the control in elevation, that is, the control of the sight angle of the antenna may be readily achieved.

In Figure 6 I have also shown a circuit for controlling the antenna position about the cross- I level or X axis. The output of a phase sensitive amplifier I68 is impressed by conductors I10 and I12 upon a relay I14 to control the servomotor which actuates the gear 82 shown in Figure 2 to rock the H-frame 32 and its associated parts. The transformer I42 is provided with a primary coil I4I across which an alternating current input is impressed by means of an alternator I43. The transformer I42 is provided with two secondary windings, one secondary winding I40 being split and furnishing an alternating current potential for the control of the input to the amplifier I58, the second secondary winding I16 of the transformer I42 is likewise provided with a center tap which is connected by conductor I18 to the phase sensitive amplifier I68 as the reference signal. A branch conductor I connects the center tap to one end of the potentiometer 96 which is associated with the vertical gyroscope, as can be seen by reference to Figure 2.- The potentiometer 12 which is carried in the housing 10 shown in Figure 2 has one end of its resistor connected to the center tap through branch conductor I82 and the conductor I 18. The other end of the resistor of the potentiometer 12 is connected by conductor I84 to one end of the secondary winding I16. The other end of the resistor of potentiometer 96 is connected by conductor I to the other end of the secondary winding I16. The brushes H and 98 of the potentiometers are interconnected by a conductor I83; and a pair of equal resistors I86 and I88. The resistor I88, however, is not connected directly to the brush H but through a brush I98 and a potentiometer I92 which is connected across the brush H and a quarter tap of the secondary. winding I18 by a conductor I94. A branch conductor I98 connects the quarter tap conductor I94 to the center. of the potentiometer resistor 12. The potentiometer resistor I2 is wound to have. a resistance proportional to the. sine of the are measured from the center tap' of the potentiometer resistor 12, and hence the voltage of the brush H is a function of. the sine of: the drift angle. Since the ends and center of. the. potentiometer sector 12 are maintained at the voltages at thetaps of the secondary winding of the transformer, a variation in voltage distribution along the resistor 12 due. to current drain by the potentiometer sector I92 is reduced to a minimum. The resistors I86 and I88 may be sufliciently high to make the effects of the current drain negligible. Since one end of the sector I92 is always at the voltage of the brush H and the other end of the resistor I92 is at the voltage of its quarter tap connection I94 as a reference voltage, the voltage of the brush I98 will be proportional to its setting multiplied by the movement of the brush II from the center tap 13 of the resistor 12. Accordingly, if the trail be set in by hand by means of the potentiometer I92 and its brush I88, the voltage of the brush I98 will be proportional to the trail multiplied by the sine of the drift angle. The rocking of the frame 32 around the crosslevel or X axis will bring the potentiometer resistor 96 which is carried for movement therewith to a balancing position by moving the sector 96 relative to the brush 98 which is being stabilized by the gyroscope 86 shown in Figure 2.

This is accomplished in a manner similar to that described above with respect to the generation of the signal by the unbalance of brushes I 46 and I I2. The signal produced by the unbalance of brushes H and 98 will appear across resistors I86 and I88 agreeable in amount and in direction to the amount and direction of the unbalance of the brushes. This signal is impressed by conductor I98 as a control signal to the phase sensitive amplifier I68.

The regulation of the antenna about the azimuth or Z axis is accomplished by the circuits shown. in Figure 6 through turn control knob 288 and drift control knob 282. The turn controlknob is used for the purpose of turning both the aircraft and the antenna. The drift control knob is used for turning only the aircraft. While maintaining the antenna at a predetermined orientation where there is a crosswind or a transverse component of target motion the maintenance of a collision course involves the establishment of a correct drift angle. This is described in the parent application Serial No. 618,448, referred to above. The turn knob 288 and the drift knob 282 are used for this purpose. The. potentiometer 88 which is shown in Figure 2, is provided with three taps 284, 286 and 288 positioned 120 apart, and a pair of brushes 2I8 and 2I2 positioned 130 apart. The brushes are connected by conductors 2M and H6 across a source of potential such as battery 2I8. The rotation of the gear 16, shown in Figure 2, relative to the. main frame 48 corresponds to a change in azimuth of the antenna relative to the aircraft. This rotation will rotate the brushes 2I8 and 2I2 around. the. resistor ring of. the

potentiometer 88, thus varying the voltage dis tribution to the taps 284, 286 and 288. A similar potentiometer 228 is provided with taps 222, 224 and 226 spaced 128 apart. Tap 2221s connected to tap 286 by a conductor 228, tap 228 is connected to tap 284 by a conductor 238, and tap 224 is connected to tap 288 by a conductor 232. A pair of brushes 234 and 236 are connected by conductors 248 and 242 to a voltmeter 244 which serves as a pilot director indicator. zero indication when approximately out of phase with the brushes H8 and 2I2 of potentiometer 88. Where the position of these brushes is varied in either direction, a correspondingv indication will be set up upon the meter 244 so that if the airplane is controlled by the pilot to maintain a zero reading upon the meter 244 the aircraft will be turned relative to the antennav which is being stabilized in azimuth through an angle controlled by the potentiometer 228. In order to reduce the errors inherent in potentiometer systems of this construction to negligible values, the potentiometer 88 is geared to the gear 16 so as to make a complete revolution in response to a turn of this gear through a fairly small angle. The knob 282 is connected to the potentiometer 228 through a gear 246 and a gear 288 which operates a shaft 258 adapted to rotate the potentiometer resistor. A complete rotation of the shaft 258 may correspond to an aircraft turn through an angle of 18 or any other suitable angle determined by the gear ratio. The effect of turning the knob 288 is, as pointed out above, to turn the aircraft and the antenna as a unit so that when the turn is completed the antenna will occupy the same position in azimuth with respect to the aircraft as it did when the turn was commenced. I accomplish this by means of the potentiometer 68 which is shown in Figure 2, and a second potentiometer 252, the resistor of which is carried by a shaft 254 and rotatable therewith. The shaft 254 is turned by a gear 256 which meshes with a gear 258 which is controlled by the knob 288. The resistor of potentiometer 68 is circular and provided with three taps 268, 262, and 264 spaced from each other and a pair of brushes 266 and 268 spaced 188 apart. The brushes 266 and 268 are connected by conductors 218 and 212 across the source of potential 2I8. The potentiometer resistor 252 is provided with three taps 214, 216, and 218 positioned 120 apart. The tap 214 is connected to the tap 262 by con: ductor 288, tap 216 is connected to the tap 268 by a conductor 282, and tap 218 is connected to the tap 264 by a conductor 284. The brushes 286 and 288 of the potentiometer 252 are positioned apart and are connected by conductors 298 and 292 to a relay 284. The relay 294 controls the servomotor 62 shown in Figure 2. The operation of potentiometers 252 and 68 is the same as the operation of potentiometers 228 and 88 just described, with the exception that the output of the brushes in one case is connected across a voltmeter and in the second case connected to control the relay 294. Whenever the knob 288 is turned it will unbalance the potentiometer 252, thus energizing the relay 294 and causing the servomotor 62 to rotate the antenna around the azimuth axis until the po tentiometer 68 is in balance with the potentiometer 252. This movement is communicated through the gear sector 18 and the gear 16 to. the potentiometer 88, thus unbalancing it.

The brushes 234 and 236 will furnish a.

with respect to potentiometer 220. This unbalance will signal a turn upon the meter 244 as pointed out above. The pilot will then operate the aircraft to bring the meter 244 back to its zero indication, and in doing so will execute a turn of the aircraft causing it to follow the antenna, so that the net result of turning knob 200 will be to turn both the aircraft and the antenna through the same angle. In this manner it is possible through knob 200 to keep the aircraft and antenna directed at the target, as will be the case in a homing or collision course. When knob 200 and knob 202 are grasped together as a unit and turned as such through a given angle, one effect will be that just described to turn both the aircraft and the antenna through a certain angle. The turning of knob 202, however, will unbalance potentiometer 220 with respect to potentiometer 80 so that. the aircraft will'be turned by the pilot in response to the signal on the meter 244 through an angle determined by the amount of unbalance of the potentiometer 220. This angle which will ,be clear is determined by the gear ratios between gears 246 and 248. The net effect of turning both knobs simultantously then is to establish a proportion between aircraft turn and antenna turn in response to a deviation from the desired course. In this manner I may establish a navigation course or a collision course at will. If a smaller ratio of aircraft turn to antenna turn than that provided by turning both knobs 200 and 202 as a unit is desired, knob 20!] may be turned at a greater rate of speed than knob 202.

It will be seen that I have accomplished the objects of my invention. I have provided a microwave antenna, a mounting therefor, and means for stabilizing the antenna about three axes disposed at right angles to each other. I have provided a stabilized microwave antenna in which conical scanning of a radar beam may beachieved while avoiding objectionable vibra tions, and in which gyroscopic forces are reduced to a minimum. I have provided a novel control means for stabilizing a microwave antenna.

It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. It is, therefore, to be understood that my invention is not to be limited to the specific details shown and described.

Having .thus described my invention, what I claim is:

1. In a microwave antenna system, means for mounting said antenna system for angular movement relative to an azimuth axis, a level and a cross-level axis, said azimuth axis and cross-level axis intersecting each other, and said level axis and said cross-level axis intersecting each other, said points of intersection being separated from each other, a microwave guide having a joint coaxial with the azimuth axis and spaced from the intersection of said azimuth axis with the cross-level axis, a joint coaxial with the cross-level axis and spaced from the intersection of the said cross-level axis with the level axis.

2. A microwave antenna, including in combination a radar antenna, an antenna gyroscope,

1 means for supporting said antenna gyroscope, means for stabilizing said support from said gyroscope, means for mounting the antenna upon said support, means for rotating said mounting means through a circular locus of small dimension with respect to the radius of gyration of said antenna whereby the rotational scanning movement of said antenna will have a reduced gyroscopic resistance due to the scanning movement.

3. A microwave antenna as in claim 2, including counter-weights moving with said antenna in a circular locus forming a system dynamically balanced about an axis parallel to and an axis transverse to the axis of rotation of said locus of scanning movement.

4. A microwave antenna, including in combination a radar antenna, means for mounting said antenna comprising a frame, a plurality of bearings carried by said frame, a plurality of cranks mounted in said bearings for rotation therein, said cranks supportingan antenna reflector, the radius of said cranks being equal and small with respect to the radius of gyration of said antenna reflector whereby gyroscopic resistance of the scanning movement of the antenna reflector is minimized.

5. A stabilized microwave antenna system, including in combination a frame, a vertical gyroscope carried by said frame, an antenna, means for mounting said antenna on said frame for pivotal movement about a level axis, a followup means interconnecting said vertical gyroscope and said antenna, a servomotor controlled by said follow-up means and carried by said frame for pivoting said antenna with relation thereto about the level axis, mounting means for carrying said frame in balanced position for pivotal movement about a cross-level axis, a cross-level follow-up means between the frame and said vertical gyroscope, a servomotor controlled by said cross-level follow-up means for pivoting said frame with relation to said frame mounting means about a cross-level axis, an azimuth gyroscope, means for supporting said frame mounting means for pivotal movement about an azimuth axis, and means controlled by said azimuth gyroscope for stabilizing said supporting means in azimuth.

6. A stabilized microwave antenna system as in claim 5, in which said cross-level follow-up means includes a drift potentiometer having a resistor, a voltage source, a center tap connection between said voltage source and the resistor of said potentiometer, a trail potentiometer having a resistor connected across the center tap connection and the brush of the drift potentiometer, a servomotor, and means for controlling said servomotor to position said frame about a cross-level axis as a function of the voltage of the brush of said trail potentiometer.

7. A control system for stabilizing a microwave antenna, including in combination means for mounting an antenna for pivotal movement about a level, a cross-level, and an azimuth axis, a servomotor for turning the antenna about an azimuth axis, an azimuth gyroscope, means responsive to movement of said antenna relative to said gyroscope for actuating said servomotor, a second servomotor for rotating the antenna about the cross-level axis, a vertical gyroscope, means responsive to relative movement between the vertical gyroscope and said antenna about the cross-level axis for actuating said second servomotor, a third servomotor for rotating said antenna about the level axis, means responsive to relative movement between said antenna and said vertical gyroscope for actuating said third servomotor to rotate said antenna about the level axis.

8. A control system as in claim 7, in which said means responsive to relative movement between said antenna and said vertical gyroscope about the cross-level axis includes a potentiometer having a brush, a second potentiometer having a brush, means for connecting said potentiometers in parallel across a source of potential, means for connecting said brushes in series with a resistor, a phase sensitive means, and a conductor connected to an intermediate point in said resistor for impressing a signal upon the phase sensitive means to control said second servomotor.

9. A control system as in claim 7, in which said means responsive to relative movement between said antenna and said vertical gyroscope about the cross-level axis includes a potentiometer having a brush, a second potentiometer having a brush, means for ccnnectingsaid pctentiometers in parallel across a source of potential, means for connecting said brushes inseries with a resistor, a phase sensitive means, and a conductor connected to an intermediate point in said re sistor for impressing a signal upon the phase sensitive means to control said second servomotor, a third potentiometer having a brush, means for supplying a potential to said third potentiometer, means for connecting said third potentiometer and its brush in series with said first resistor, the construction being such that the third potentiometer brush may be set to introduce a correction which is a function of the sine of the drift angle.

10. A control system as in claim 7, in which said means responsive to movement of said mountin relative to the azimuth gyroscope includes a circular potentiometer provided with three taps positioned 120 apart and a pair of brushes positioned 180 apart, a second potentiometer of similar construction having its taps connected in parallel with the taps of said first circular potentiometer, the brushes of said second potentiometer being connected to a phase sensitive means adapted to control the servomotor for turning the antenna about the azimuth axis.

11. A control system as in claim 7, in which said means responsive to movement of said mounting relative to the azimuth gyroscope includes a circular potentiometer provided with three taps positioned 120 apart and a pair of brushes positioned 180 apart, a second potentiometer of similar construction having its taps connected in parallel with the taps of said first circular potentiometer, the brushes of said second potentiometer being connected to a phase sensitive means adapted to control theservomotor for turning the antenna about the azimuth axis,

a third circular potentiometer having three taps positioned 120 apart and a pair of brushes positioned 180 apart, means responsive to the movement of said antenna in azimuth for rotating the brushes of said third potentiometer, a fourth circular potentiometer having three taps positioned apart connected in parallel with'taps of said third potentiometer, said fourth potentiometer having a pair of brushes positioned apart and conductors connecting said brushes across a voltmeter.

12. A control system as in claim 7, in which said means responsive to movement of said mounting relative to the azimuth gyroscope includes a circular potentiometer provided with three taps positioned 120 apart and a pair of brushes positioned 180 apart, a second potentiometer of similar construction having its taps connected in parallel with the taps of said first circular potentiometer, the brushes of said second potentiometer being connected to a phase sensitive means adapted to control the servomotor for turning the antenna about the azimuth axis, and manual means for moving the resistor of said second circular potentiometer relative to its brushes.

13. A control system as in claim 7, in which said means responsive to movement of said mounting relative to the azimuth gyroscope includes a circular potentiometer provided with three taps positioned 120 apart and a pair of brushes positioned 180 apart, a second potentiometer of similar construction having its taps connected in parallel with the taps of said first circular potentiometer, the brushes of said second potentiometer being connected to a phasesensitive means adapted to control the servomotor for turning the antenna about the azimuth axis, a third circular potentiometer having three taps positioned 120 apart and a pair of brushes positioned 180 apart, means responsive to the movement of said antenna in azimuth for rotating the brushes of said third potentiometer, a fourth circular potentiometer having three taps positioned 120 apart connected in parallel with taps of said third potentiometer, said fourth potentiometer having a pair of brushes positioned 180 apart and conductors connecting said brushes across a voltmeter, and manual means for moving the resistor of said fourth circular potentiometer relative to its brushes.

CARL L. NORDEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 299,183 Tucker May 27, 1864 1,296,303 Manly Mar. 4, 1919 1,696,468 Buhr Dec. 25, 1928 1,732,677 Fieux Oct. 22, 1929 1,768,966 Tanner July 1, 1930 2,407,275 Hays Sept. 10, 1946 2,410,831 Maybarduk et a1. ,Nov. 12, 1946 2,412,612 Godet Dec. 17, 1946 2,415,679 Edwards et al Feb. 11, 1947 2,423,438 Dawson July 8, 1947 

